In current technology, oxidation of the peritoneum is monitored by measuring the intra-abdominal carbon dioxide level and hemal bicarbonate by using discrete blood and buffer liquid samples.
The concentration of a patient's inner organ gas, especially CO2, is measured by drawing samples from the vicinity of this inner organ, e.g. from the abdomen, said samples being analyzed in a laboratory analyzer. According to the solution described in U.S. Pat. No. 4,643,192, the sampling is effected by means of a catheter. The catheter consist of a sampling element, having a wall through which the gas is absorbed into a salt solution contained inside the catheter and which wall is not permeable to a liquid component, and of a tube for aspirating a sample from the sample chamber and for delivering a fresh salt solution into the sample chamber. The aspiration and supply of a liquid into the tube and sample chamber is effected by means of a syringe connected to a special fitting mounted on the end of the tube. The liquid contained in the sampling element must be allowed a relatively long time, e.g. half an hour, for the interaction with an outside gas to be measured in order to provide a sufficient time for the gas to absorb through the sampling element wall and to reach an equilibrium. This is followed by aspirating the liquid out of the catheter into the syringe and by taking it to a laboratory for analysis for the determination of the concentration of a gas diffused through the catheter wall.
A problem in this type of solution is the execution of the measurement of a gas penetrated through the catheter wall, the method being inconvenient and tedious. This tediousness and inconvenience is further emphasized by the fact that every time the catheter is exhausted of liquid by suction said catheter must be refilled with fresh liquid, which must be allowed to stay in the catheter for a sufficiently long time in order to reach a gas equilibrium before it is aspirated out and transferred for analysis.